Generally, two-component polyurethane resin coatings comprise a polyisocyanate prepolymer composition as a hardener and a polyol composition as a base resin and have a very high wear resistance, chemical resistance, stain resistance and flexibility.
Conventionally, aliphatic polyisocyanates obtained from aliphatic diisocyanates have been used in polyisocyanate prepolymer compositions as hardeners, and acrylic polyol, polyester polyol, fluoropolyol, etc. have been widely used as polyol compositions.
A polyurethane resin coating using aliphatic polyisocyanate prepolymers is especially excellent in weather resistance, and thus, a demand therefor grows larger in the fields of automobiles, plastics, and exterior materials for constructions.
When a two-component polyurethane resin coating is formulated by using aliphatic polyisocyanate prepolymers as a hardener and a hydroxyl group-containing polyol as a base resin, the coating layer formed contains many urethane bonds and has improved in weather resistance, wear resistance, chemical resistance, solvent resistance, stain resistance, water resistance, heat stability, etc. and better coating characteristics. Because of these characteristics, it is considered that this two-component type polyurethane resin coating will come into wide use in the fields where excellent properties of coating layers are necessary, for example, coating or repair of automobile bodies and a variety of plastics.
Aliphatic polyisocyanates obtained from aliphatic diisocyanate include biuret polyisocyanates, adduct polyisocyanates, and isocyanurate group-containing polyisocyanates. Among these, isocyanurate group-containing polyisocyanates provide superior weather resistance, wear resistance, chemical resistance, stain resistance, flexibility and heat stability than other aliphatic polyisocyanates.
However, isocyanurate group-containing polyisocyanates lack compatibility with the hydroxyl group-containing polyol compositions, and therefore do not provide coating layers having stable properties. Under such a circumstance, there is a demand for development of aliphatic polyisocyanate prepolymers comprising an isocyanurate group-containing polyisocyanate having improved compatibility with hydroxyl group-containing polyols.